It is currently possible to transmit audiovisual programs in digital form via broadcasting networks of the microwave (herzian), cable, satellite type, etc. or via telecommunication networks of the DSL type (Digital Subscriber Line) or BLA type of (Local Radio Loop) or via DAB networks (Digital Audio Broadcasting) as well as via any wireless telecommunication network of the GSM, GPRS, UMTS, Bluetooth, WiFi types, etc. These works are frequently encrypted or scrambled by various well known means to avoid pirating.
As concerns the distributed systems based on the client-server principle characterized by “caching,” the prior art also contains two main types of systems that are classified according to the content treated by this “caching.” The term “caching” denotes the possibility of being able to temporarily hold a copy of contents or of data (permanently stored in a central server) at a point or at different points of the network (e.g., local servers) to serve the requests of clients the closest to these points, thus reducing the overload on the server from contents and consequently optimizing the transmission rate used at the access points.
The first type processes data whose distribution has no time restrictions (systems for the distribution of files by “caching”) and the second type concerns the processing of multimedia (audio/video) data.
The systems for conventional distributed files such as Sun NFS, Apollo Domain, Andrew, IBM AIX, DS, AT&T RFS perform the “caching” of files locally, do not have the possibility of making the “caching” of files in proximate or remote nodes and cannot allocate local servers for applying the “caching” to files. Moreover, the conventional distributed systems characterized by “caching” have a granularity of the size of a file and consequently the possibilities of having a scalability of the distribution of the contents via the network is greatly reduced.
On the other hand, other distributed multimedia systems characterized by “caching” such as the “Berkeley Distributed VOD,” for example, do not obtain a “caching” that is completely secure and personalized for each user and also have limited capacities of scalability while frequently being penalized by the limited bandwidth of the networks.